This invention pertains to the art of semiconductor junction formation.
Formation of semiconductor junctions in silicon webs, such as dendritic silicon webs for use as photovoltaic solar cells, for example, is typically carried out in a tube-type or belt-type diffusion furnace. If junctions are to be formed in both faces of the web, a two-step process is required in which a dopant layer is first diffused into one face, the face is then cleaned and masked as with silicon dioxide, SiO.sub.2, to prevent cross-over of dopant from the diffused layer to the to-be-diffused layer at the opposite face and then, in a separate operation, another dopant layer is diffused into the opposite face. The heat-up to, say, 850.degree.-950.degree. C. and the subsequent cool-down for each separate layer may typically take 40 minutes or so.
It is the aim of this invention to provide a process for forming semiconductor junctions which is significantly faster, less complicated and less expensive and is particularly well adapted to forming junctions simultaneously in both faces of dendritic web silicon for solar cell applications. An important aspect of the invention is that the heat required to diffuse in the dopants is supplied by a relatively short duration pulse of high intensity light.